This invention relates to an aluminum alloy bearing for use mainly in an internal combustion engine of an automobile which bearing exhibits an excellent fatigue resistance even under such severe conditions of use as being compact in size and lightweight design for fuelsaving purposes, or as a high-speed or a high-engine speed design for achieving a high performance.
Al--Sn alloy, Al--Si--Sn alloy, Al--Zn alloy and Al--Zn--Si alloy have heretofore been used to form an aluminum alloy bearing for an internal combustion engine. Particularly, a bearing of an Al--Zn--Si alloy related to the present invention is disclosed in Japanese Patent Application No. 1-140284 filed earlier by the assignee of the present application.
Recently, however, as regards the condition of use of internal combustion engines, a compact and lightweight design for fuel-saving purposes as well as a high output design has been required, and the engines have been used in a more severe environment as at higher temperatures, at higher speed and under a higher load. As a result, the fatigue resistance achieved by the conventional bearing material, such as Al--Sn alloy, Al--Si--Sn alloy, Al--Zn alloy and Al--Zn--Si alloy, has become inadequate.
Moreover, in the case of the conventional material, such for example as the Al--Si--Cd alloy, when an overlay becomes worn, a problem with respect to a seizure resistance arises, and also the special element, Cd, contained in the material, poses a problem from the viewpoint of pollution. In an internal combustion engine designed for making it possible to operate at high speed under a high load, a film of lubricating oil becomes thin, so that a fatigue resistance and a seizure resistance become inadequate. The earlier-filed Japanese Patent Application No. 1-140284 is directed to an invention which improves such inadequate fatigue resistance and seizure resistance; however, this earlier invention has now become insufficient in fatigue resistance under more severe conditions of use.